Principle of the periscope. A - Periscope using two plane mirrors. B - Periscope using two right–angled prisms. 1 - 2 - Plane mirrors. 3 - 4 - Right–angled prisms. 5 - 6 - Observer eye. 7 - 8 - Periscope tube. H - Periscope optical height.
Principle of the lens periscope.A - Periscope using a single lens (L2) to correct image.B - Periscope which uses two lenses (L2-L3) to correct image.1-3 - Periscope window.2-4 - Field stop or reticle.P - Right–angled prisms (or plane mirrors).L1 - Objective lens.L2 - for A - L2 - L3 - for B - Image erecting lens.L3 - L4 -for A - L4-L5- for B - Eyepiece.L0 - Field lens.y - Distant object.H - Periscope optical height.